This invention relates to infrared vidicon systems, and more particularly to systems of this type which utilize vidicon tubes having capacitive-sensitive target surfaces.
All capacitive vidicon image tubes, for example one having a pyroelectric target surface, require some type of optical modulation of the infrared scene in order to produce a visible picture. This is the case because of the target area of the infrared vidicon tube, which is a series of capacitors which inherently cannot provide a DC response due to charge leakage. The optical modulation may be provided by panning the pyroelectric vidicon camera over the scene, by nutating the camera lens, or by chopping the scene, using a conventional radiation chopper.
Panning or nutating the camera over the scene produces thermal lag on the pyroelectric vidicon sensitive surface which produces undesirable image "ghosts" or "tails" trailing behind the image in the direction of the panning or nutating. This can be overcome, for stationary objects only, by utilizing chopping means with a 50% duty cycle. Moving targets in a 50% duty cycle chop system, however, exhibit increased signal which introduces errors where absolute radiometric signal readout is required. Another disadvantage of the 50% duty cycle chop system is that such a system inherently generates only about one half of the signal that the systems utilizing panning or nutating provide.
Another problem associated with capacitive target element vidicons such as pyroelectric vidicons is the lack of uniform responsivity across the capacitive elements or sensitive target area of the vidicon tube.
It is an object of this invention to provide a new and improved infrared vidicon system which overcomes some of the disadvantages associated with such systems.
A further object of this invention is to provide an improved infrared vidicon system having greater signal output than conventional chopped systems of this type, while overcoming the disadvantages of the systems using panning or nutating for modulating the scene.
A further object of this invention is to provide a new and improved vidicon system which produces quantitative data with respect to the temperature of an object in the field of view of the system.